In radiological interventional procedures an instrument like a catheter is navigated through the body of a patient under continuous X-ray observation. The U.S. Pat. No. 5,255,680 describes for such procedures an examination apparatus that localizes the current position of the catheter tip with the help of radiofrequency markers and then positions the X-ray apparatus automatically in such a way that the catheter is always in the field of view. One disadvantage of this approach is the need of additional markers on the instruments. Moreover, the generated projections are often insufficient for the navigation of a catheter through a complicated vessel geometry.